Coating a layer of a material on a surface of cathode active material particles is a common method to modify the cathode active material of a lithium ion battery. For example, coating a carbon layer on the surface of lithium iron phosphate particles can effectively solve the low electrical conductivity problem of the lithium iron phosphate to achieve better electrical conductivity. In another example, coating a surface of lithium cobalt oxide particles or other cathode active material particles with aluminum phosphate can improve a thermal stability of the cathode of the lithium ion battery (referring to “Correlation between AlPO4 nanoparticle coating thickness on LiCoO2 cathode and thermal stablility.” J.Cho, Electrochimica Acta 48 (2003) 2807-2811 and U.S. Pat. No. 7,326,498).
In a conventional method for coating the aluminum phosphate on the cathode active material, aluminum phosphate particles are dispersed in water to form a dispersion liquid, the cathode active material particles are added in the dispersion liquid, the aluminum phosphate particles are adsorbed on the surface of the cathode active material particles due to adsorption effect, the water in the dispersion liquid is dried, and the resultant solid is heated at 700° C. to form the cathode active material having the aluminum phosphate particles on the surface thereof. However, because the aluminum phosphate is insoluble in water, the aluminum phosphate coating layer formed on the surface of the cathode active material by the above method is not uniform, resulting in a relatively poor cycling performance of the lithium ion battery.